Functions 1.Movement -Whole body or parts of the body 2.Maintenance of body posture. 3.Separates body cavities. 4. Respiration. Muscular Tissue

In animals there are two principle types of muscles: 1.Striated muscles –their cells exhibit cross striations under light microscopy. Based on the location striated muscles are further divided into: a. Skeletal muscle b. Cardiac 2. Smooth muscle. These cells have no cross striations.

Myocytes / Muscle cells These are the cells of the muscle tissue. They are elongated cells whose primary role is contraction.

Skeletal Muscle Skeletal muscles are anchored by tendons or by aponeurosis to bone. Responsible for movement of the skeleton, maintenance of body posture.

Voluntary-control of will. Components of skeletal muscle tissue. a. Muscle cells. These are long unbranched cells (run parallel) or myofibres. Have several peripherally located nuclei. b.Supportive connective tissue.

The skeletal muscle cells are multinucleated. Their nuclei are located in the cytoplasm immediately beneath the plasma membrane=sarcolema Each myofibre appears striated. That is, they have periodic transverse bands. Within a myofibre are myofibrils.

Skeletal muscle-longitudinal and transverse sections.

Myofibrils This is the basic contractile unit. Several myofibrils are located within a muscle fibre. They give the muscle fibre the appearance of cross striations.

They are made up several sarcomeres each of which runs from one z band to the next. They extend the entire length of a muscle cell. When muscle contracts each sarcomere shortens and thickens.

Myofilaments These are the actual contractile elements of skeletal muscle. Bundle of myofilaments make a myofibril. Two types of myofilaments are associated with muscle contraction. 1. Thin filaments. Composed of protein actin 2. Thick filaments. Composed of protein myosin II. The two myofilaments occupy most of the cytoplasm =sarcoplasm.

Cross striations Arrangement of thick and thin filaments results in the different densities in the sarcomere=cross striations. Under the light microscope, they appear as alternate light and dark bands=termed as A band and I bands.

The A and I bands are bisected by narrow regions of contrasting density. The light I band is bisected by the Z line while the thick A band is bisected by the M band.

Skeletal muscle cells- Longitudinal section

Connective tissue in Muscle Several myofibres are grouped together to form a fasciculus (bundle). Myofibre- endomysium Fasciculus- perimysium Whole muscle- epimysium

Cardiac muscle tissue It is found in the heart. Controlled by the autonomic nervous system (ANS)- involuntary. 1. Muscle has short striated cells. 2. Fibres branch and anastomose with adjacent fibres.

3. Each cell has 1-2 nuclei which are centrally located unlike the skeletal muscles where the cells are multinucleated with their nuclei located below the plasma membrane.

4. Have intercalated discs which are specialized intercellular junctions where one cell touches another cell. They appear densely staining under the light microscope.

–During Increased demand the cardiac cells can hypertrophy. –During decreased demand the muscle undergoes atrophy

Ca rdiac muscle tissue

Intercalated discs

PURKINJE FIBERS Specialized cardiac fibers. Involved in impulse conduction to the various parts of the myocardium. Larger than the cardiac muscle cells. Myofibrils in these fibres are fewer than in the typical cardiac muscle. They are star-like in shape. They are lighter staining when compared with normal cardiac cells.

PURKINJE FIBERS (cross-section) Cardiac cells Purkinje fibres

Smooth Muscle Tissue Location They line blood vessel walls, the stomach, the intestines and urinary bladder. They are involuntary. They have no cross striations. They are referred to as either; –Smooth, un-striped, visceral or plain muscles.

Structure - Smooth muscle is formed by union of spindle shaped cells. The cells are elongated and taper on both ends. - The nuclei are centrally located. -The cells are interconnected by gap junctions.

Smooth Muscle cells -Longitudinal section a). b).

Smooth Muscle cells – Longitudinal & cross section

Skeletal musclecardiac musclesmooth muscle Location Muscles of the skeleton, tongue, oesophagus and diaphragm. Heart, superior and inferior vena cava, pulmonary veins. Blood vessels, intestines, stomach. Fibers long and unbranched Short and branching spindle Nuclei Few and peripheral Single and central Sarcomerespresent None Cell to cell junctions None Intercalated discs. Gap junctions